A wheel loader is provided with a vehicle body, and a work implement attached to the vehicle body. The work implement has a boom and a work tool. The boom is rotatably attached to the vehicle body. The work tool is, for example, a bucket, a fork, or the like, attached to the distal end of the boom.
As disclosed in Japanese Laid-Open Patent Application 2010-265639, a work implement is provided with a link mechanism, such as a parallel link mechanism, a Z bar link mechanism, or the like. The link mechanism is a mechanism that couples the boom and the work tool, and operates the work tool in interlocking fashion with operation of the boom. In a wheel loader outfitted with a Z bar link mechanism, as the boom rotates upward, the angle of the work tool varies with respect to the horizontal direction. However, when, for example, the bucket is raised high with the bucket in a loaded state, it is preferable for the angle of the bucket to be maintained on the horizontal.
Accordingly, a parallel link mechanism is designed to change the relative angle of the bucket with respect to the boom as the boom is rotated upwards, so as to maintain the angle of the bucket on the horizontal. In addition to the parallel link mechanism mentioned above, link mechanisms having a function of keeping to a low level variation of the angle of the bucket with respect to the horizontal direction as the boom is rotated upwards (hereinafter termed an attitude-retention function) are known as well. In the following description, the term “parallel link mechanism” is not limited to parallel link mechanisms in the narrow sense, and includes other link mechanisms having an attitude-retention function.